I'm leaning towards (A) in my theory (the return hose is not getting as hot as it should making me think that the inlet to the pump is partially blocked, because I've flushed out the Core with a garden hose, did it last night when it was 6°)

Heat will get "hot" at high engine rpm but not at normal operating rpm's, (only gets fairly warm)

the heater core is plumbed into the water pump suction side, and to the water outlet area before the thermostat...so flow is from hot just before thermostat thru heater core to intake side of water pump...coolant is pulled by water pump and pushed out into block and heads...
probably cause of low heat output from heater
1. failed stuck open thermostat...radiator return tank should get too hot to keep hand on...indicated by your comments that engine runs cool
2. air dam in core> purge per Aero forum previous posts or see Ford service cd
3. mineral deposit plugging of heater core...common in areas with high mineral content in water...not removeable by reverse flushing...can be seen in radiator tank crossflow tube ends

does your engine overheat easily?>look for water pump impeller damage-failure

where the coolant comes out of the engine there is a thermostat that is closed when the engine is cold and at this point and forces water to go to the heater core. so the coolant is pushed into the heater core and the return goes back into the pump in take.
so you either have a bad thermostat stuck open or a blockage

On a '93 going into the "suction" side (top) of the water pump, the heater core return hose flairs dramatically to go over the inlet stem.

The interior of that hose just above the flair had seperated and was collapsing under suction, which was reducing the flow substantially.

This was kind of my theory behind my question. Since I had flow through the block and the Heater core and high engine rpms was producing more heat, I was figuring something was blocking the water pump inlet,(draw side) but wasn't sure what (stop leak, sediment, foreign object etc.)

It's still not as hot as I remember it being, but it's better, I just need to replace that hose now.

If I remember correctly, the high pressure side is on top of the engine, near the thermostat and the low pressure side is near the water pump. The high pressure side should go to the bottom of the heater core for proper purging of the air from the heater core. Otherwise, air will be trapped inside the heater core, giving you less heat than it should.

The hoses in a closed system should be under constant pressure any time the coolant has reached operating temperature and expanded - a collapsed hose shouldn't be possible unless you have leaks or a failed radiator cap.

Well, a hose collapseing is very possible, because the system may be under constant pressure, but there is still a pressure differential before and after the pump. If the hose is seperateing, the inner layer may collapse, but the hose itself does not collapse as a whole.

Well, a hose collapseing is very possible, because the system may be under constant pressure, but there is still a pressure differential before and after the pump. If the hose is seperateing, the inner layer may collapse, but the hose itself does not collapse as a whole.

That is correct.

I think what is important to keep in mind is the location of failing inner wall of the hose and the fact that it wasn't collapsing it was being sucked into the inlet, causing a 'restriction" of flow not an elimination of flow.

collapsing suction hoses are the main reason the water pump intake house from the radiator usually has an interior coil to keep it open in proper hose designs. lower hose on Aero...
interior heater hose breakdown goes unnoticed in heater hoses because most owners don't examine them for softness or imperfections along length.

collapsing suction hoses are the main reason the water pump intake house from the radiator usually has an interior coil to keep it open in proper hose designs. lower hose on Aero...
interior heater hose breakdown goes unnoticed in heater hoses because most owners don't examine them for softness or imperfections along length.

96_4wdr:

The strange thing is that most replacement lower radiator hoses do NOT come with that spring. I had to reuse the old spring inside every time I replace that lower hose. I do that every couple of years regardless of how the hose looks. Just a precaution against being stuck on the side of the road on a vacation trip.

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